This invention relates to strain transducers of the type employing piezoresistive sensing devices formed in a semiconductor wafer.
As is known, there exists a wide variety of semiconductor pressure transducers employed for sensing pressure or force. As such, the transducers are employed in a wide range of applications and are used in the aerospace, automotive, and medical fields.
Many such transducers employ piezoresistive devices which in general, exhibit a change in resistance which is proportional to the magnitude of an applied force. These transducers are fabricated by employing conventional semiconductor techniques and hence, are amenable to mass production in regard to semiconductor technology. As such, the piezoresistive sensor may be bonded or diffused into a diaphragm which is fabricated from a semiconductor material such as silicon.
A sensing element in conjunction with the diaphragm is usually coupled or secured to a housing; which housing serves as a support for the diaphragm and furthermore, enables the routing of leads associated with the sensing elements to enable monitoring of a pressure or a force in an environment. In many such applications, the coupling of the device or diaphragm assembly to the housing can constitute a significant problem. This is due to the fact that based on the multitude of various environments in which the transducer must operate, the bonding of the diaphragm to the housing requires a hermetic seal.
The seal between the diaphragm and housing in essence, should be leak-free and hence, prevent deleterious substances which may be present in the environment from attacking or otherwise interfering with the terminals and sensor components. Furthermore, the nature of the seal specifies that the transducer assembly possesses a surface which is continuous as defined by the geometrical form of the housing and must present a flat bondable surface to thus avoid any ridges or flaws which will affect the quality of the seal between the transducer and housing.
In any event, in combination with a high quality seal is the further aspect of enabling the connection of wires to terminals associated with the transducer and to make such connections simply and reliably and without interfering with the seal or the housing bonded to the diaphragm assembly. Thus, there are many patents in the prior art which attempt to solve these problems.
However, coupled with the above noted problem is the further obvious aspect of producing a device which is economical to manufacture and reliable in operation. It is furthermore desireable to provide such a device which is protected from deleterious or corrosive substances contained in the force emitting environment and which otherwise may undesirably attack or erode the transducer, diaphragm and associated sensors and terminals.
It is therefore an object of the present invention to provide an improved transducer assembly employing piezoresistive sensors secured to semiconductor diaphragms; which structures incorporate relatively flat bondable areas to enable hermetic coupling to a suitable housing, while employing protected lead and terminal configurations associated with the sensor devices associated with the transducer.